Oil wells are drilled from the surface of the earth down to and through hydrocarbon bearing formations to allow recovery of the hydrocarbons through the well. The wells are often cased down to the producing formation. The well may be cased or lined with a metal liner through the producing formation or may be left in open hole condition in the producing formation, i.e. without a casing or liner. If a well is cased or lined in the producing formation, the casing or liner is typically perforated to allow hydrocarbons to flow from the formation into the well for production.
In many wells, whether cased and perforated or left in open hole condition in the productive formations, particulates, e.g. sand, may flow from the formation with the produced hydrocarbons. The produced sand may erode and otherwise damage metal liners, casing, valves, etc. and must be removed from the produced fluids at the surface and then safely disposed of. To minimize sand production, it is common practice to gravel pack such wells as part of the completion process.
A gravel packing system typically includes a filter element, e.g. a wire wrapped screen, that is positioned in the well near a productive formation, e.g. adjacent perforations. The screen is carried into a well on a work string that includes a packer that seals the annulus between the work string and a cased portion of the well above the productive formation. A slurry of gravel packing liquid and particulates, typically referred to as gravel, may then be flowed down the work string. A cross over device is normally included to direct the slurry flow from inside the work string above the packer to the annulus around the screen below the packer. The screen allows the liquid to flow into the interior of the screen, but blocks the flow of the particulates to fill the annulus around the screen with the particulates, i.e. to gravel pack the annulus. The liquid flows back up the work string to the crossover, where it is directed into the annulus above the packer and may be returned to the surface location of the well.
Gravel packing is normally done in an overbalanced condition, i.e. with the pressure in the well at the screen higher than the natural formation pressure. Borehole fluids therefore tend to flow into the formation. To avoid fluid loss and possible formation damage, a fluid loss device may be included in a gravel packing work string between the screen and the packer. A fluid loss device typically includes some type of valve, e.g. a ball valve or a flapper valve, that may be closed when gravel packing is completed. The valve may be closed when a wash pipe is withdrawn from the assembly after the gravel packing operation. The closed valve isolates the productive formation from borehole pressure and fluids above the valve. This allows the well fluids to be circulated, e.g. to remove any remaining particulates or other treating fluids, without losing fluids into the formation. When production tubing has been installed in the well, the fluid loss valve is typically opened permanently to allow production of hydrocarbons through the valve and up the production tubing.
Such fluid loss devices may also be useful with other well treatment systems and processes. For example, filter cake in an open hole completion may prevent large fluid losses. It is normally desirable to remove the filter cake before producing the well, for example by an acidizing treatment. After the filter cake is removed, fluid losses may be a problem. Therefore, it may be desirable to include a fluid loss device in such treatment systems to limit fluid losses in the productive zone while the well is circulated to remove any treating fluids, e.g. acid, from the well above the producing formation.